1. Field of the Invention
The present invention relates generally to the removal of head covers from coke drums, and more particularly to devices and methods for the safe removal of bottom head covers from coke drums.
2. Description of the Related Art
Coke drums are vertical pressure vessels used in the refining of crude oil for the coking of various heavy hydrocarbon materials. The coking process generally involves placing petroleum residues inside the coke drum and cracking them into light products and a solid coke residue. This is accomplished by exposing the residues to elevated temperatures (typically approximately 900xc2x0 F.) and pressures (typically approximately 10 to 30 psig).
Coke is a hard, coal-like substance which builds up inside the coke drum during the coking process. Once the coke drum is full of coke, the coke drum is xe2x80x9cdecokedxe2x80x9d by introducing steam and water into the coke drum to quench the temperature to approximately 200xc2x0 F. The quench water is then drained via piping to a storage tank. After draining the quench water, the top head and bottom head of the coke drum are removed (or xe2x80x9cdeheadedxe2x80x9d) to provide access to the inside of the coke drum. The coke is then cut away using high pressure hydraulic drilling, permitting it to fall from the coke drum into a chute positioned at the bottom opening to direct the removed coke to a desired location.
The loosening and removal of the bottom head entails risk to personnel in the vicinity of the bottom head during deheading. In this regard, the quench water, hydrocarbon material, and coke remaining inside the coke drum are still quite hot after the quench water is drained. Accordingly, when the residual quench water is drained through the loosened bottom head cover, the hot quench water and steam pose a risk to personnel in the area. In addition, the quench water, hydrocarbon material and loose coke resting on the bottom head cover are quite heavy. The weight of these materials can result in the failure of the equipment or other structures supporting the bottom head cover as it is removed, thereby posing an additional potential risk.
Accordingly, a need has existed for a device and method for the removal of the bottom head cover of a coke drum that is relatively easy to use, reduces risks and maximizes the safety for the operator. The present invention satisfies these and other needs and provides further related advantages.
The present invention provides a coke drum bottom head removal system for removing a bottom head attached by fasteners to a bottom head flange of a coke drum. The system comprises a carriage that is positionable beneath the bottom head cover, and a cart mounted on the carriage that can be moved vertically between a raised position and a lowered position. The system also comprises a plurality of clamps and supports mounted on the cart. In accordance with the invention the system is operable from a remote location to reduce risks and maximize safety for the operator.
In the preferred embodiment, the carriage is suspended by trolleys from a pair of overhead tracks positioned along opposite sides of the bottom head cover. The cart is preferably suspended from an upper portion of the carriage by a plurality of hoists. These hoists are operated to raise and lower the cart with respect to the carriage when the carriage is positioned beneath the bottom head cover.
Each of the clamps mounted on the cart comprises an upper clamping surface, such as a fixed jaw, adapted for engagement with the bottom head flange. Each clamp also comprises a lower clamping surface, such as a movable ram, adapted for engagement with the bottom head cover. The clamps are actuated between a closed position, in which the clamping surfaces apply a compressive force that maintains a substantially tight fluid engagement between the bottom head flange and the bottom head cover upon removal of the fasteners, and an opened position, in which the clamping surfaces are moved apart to permit a limited spacing between the bottom head flange and the bottom head cover when the fasteners are removed.
In use, the carriage is positioned beneath the bottom head cover, with the cart in the lowered position. A plurality of the fasteners connecting the bottom head cover to the bottom head flange are removed, exposing fastener holes. The cart is then moved to the raised position such that the supports are inserted into a plurality of the fastener holes. The clamps are then positioned for engagement with the bottom head cover and the bottom head flange and moved to the closed position.
With the clamps in the closed position, the remaining fasteners are removed. The compressive force applied by the clamps maintains a substantially fluid tight engagement between the bottom head flange and the bottom head cover when the fasteners are removed. Since the fasteners are removed manually, the clamps ensure operator safety while the fasteners are being removed.
Once the fasteners are removed, the operator, from a remote location, reduces the compressive force applied by the clamps, moving them to the opened position. This allows the bottom head cover to be lowered onto a support surface of each support. The lowering of the bottom head cover creates a space between the bottom head cover and the bottom head flange through which residual quench water drains.
When the quench water and other materials in the coke drum have drained, the cart is moved to the lowered position. This disengages the supports from the fastener holes in the bottom head flange, with the bottom head cover remaining on the cart and supported by the supports. The carriage can then be moved to transport the bottom head cover away from the bottom head to permit further decoking of the coke drum.
Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.